[Fixed Point Arithmetic] Fixed Point and Integer Conversions

This patch includes the necessary code for converting between a fixed point type and integer.
This also includes constant expression evaluation for conversions with these types.

Differential Revision: https://reviews.llvm.org/D56900

llvm-svn: 355462

clang/include/clang/AST/OperationKinds.def

@@ -200,6 +200,14 @@ CAST_OPERATION(IntegralToFloating)
 ///    (_Accum) 0.5r
 CAST_OPERATION(FixedPointCast)
 
+/// CK_FixedPointToIntegral - Fixed point to integral.
+///    (int) 2.0k
+CAST_OPERATION(FixedPointToIntegral)
+
+/// CK_IntegralToFixedPoint - Integral to a fixed point.
+///    (_Accum) 2
+CAST_OPERATION(IntegralToFixedPoint)
+
 /// CK_FixedPointToBoolean - Fixed point to boolean.
 ///    (bool) 0.5r
 CAST_OPERATION(FixedPointToBoolean)

clang/include/clang/Basic/FixedPoint.h

@@ -141,13 +141,26 @@ class APFixedPoint {
     return APFixedPoint(Val << Amt, Sema);
   }
 
+  /// Return the integral part of this fixed point number, rounded towards
+  /// zero. (-2.5k -> -2)
   llvm::APSInt getIntPart() const {
     if (Val < 0 && Val != -Val) // Cover the case when we have the min val
       return -(-Val >> getScale());
     else
       return Val >> getScale();
   }
 
+  /// Return the integral part of this fixed point number, rounded towards
+  /// zero. The value is stored into an APSInt with the provided width and sign.
+  /// If the overflow parameter is provided, and the integral value is not able
+  /// to be fully stored in the provided width and sign, the overflow parameter
+  /// is set to true.
+  ///
+  /// If the overflow parameter is provided, set this value to true or false to
+  /// indicate if this operation results in an overflow.
+  llvm::APSInt convertToInt(unsigned DstWidth, bool DstSign,
+                            bool *Overflow = nullptr) const;
+
   void toString(llvm::SmallVectorImpl<char> &Str) const;
   std::string toString() const {
     llvm::SmallString<40> S;
@@ -175,6 +188,14 @@ class APFixedPoint {
   static APFixedPoint getMax(const FixedPointSemantics &Sema);
   static APFixedPoint getMin(const FixedPointSemantics &Sema);
 
+  /// Create an APFixedPoint with a value equal to that of the provided integer,
+  /// and in the same semantics as the provided target semantics. If the value
+  /// is not able to fit in the specified fixed point semantics, and the
+  /// overflow parameter is provided, it is set to true.
+  static APFixedPoint getFromIntValue(const llvm::APSInt &Value,
+                                      const FixedPointSemantics &DstFXSema,
+                                      bool *Overflow = nullptr);
+
 private:
   llvm::APSInt Val;
   FixedPointSemantics Sema;

clang/lib/AST/Expr.cpp

@@ -1718,6 +1718,8 @@ bool CastExpr::CastConsistency() const {
   case CK_ZeroToOCLOpaqueType:
   case CK_IntToOCLSampler:
   case CK_FixedPointCast:
+  case CK_FixedPointToIntegral:
+  case CK_IntegralToFixedPoint:
     assert(!getType()->isBooleanType() && "unheralded conversion to bool");
     goto CheckNoBasePath;
 

clang/lib/AST/ExprConstant.cpp

@@ -9776,6 +9776,7 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
   case CK_AddressSpaceConversion:
   case CK_IntToOCLSampler:
   case CK_FixedPointCast:
+  case CK_IntegralToFixedPoint:
     llvm_unreachable("invalid cast kind for integral value");
 
   case CK_BitCast:
@@ -9810,6 +9811,19 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
     return Success(IntResult, E);
   }
 
+  case CK_FixedPointToIntegral: {
+    APFixedPoint Src(Info.Ctx.getFixedPointSemantics(SrcType));
+    if (!EvaluateFixedPoint(SubExpr, Src, Info))
+      return false;
+    bool Overflowed;
+    llvm::APSInt Result = Src.convertToInt(
+        Info.Ctx.getIntWidth(DestType),
+        DestType->isSignedIntegerOrEnumerationType(), &Overflowed);
+    if (Overflowed && !HandleOverflow(Info, E, Result, DestType))
+      return false;
+    return Success(Result, E);
+  }
+
   case CK_FixedPointToBoolean: {
     // Unsigned padding does not affect this.
     APValue Val;
@@ -9970,6 +9984,20 @@ bool FixedPointExprEvaluator::VisitCastExpr(const CastExpr *E) {
       return false;
     return Success(Result, E);
   }
+  case CK_IntegralToFixedPoint: {
+    APSInt Src;
+    if (!EvaluateInteger(SubExpr, Src, Info))
+      return false;
+
+    bool Overflowed;
+    APFixedPoint IntResult = APFixedPoint::getFromIntValue(
+        Src, Info.Ctx.getFixedPointSemantics(DestType), &Overflowed);
+
+    if (Overflowed && !HandleOverflow(Info, E, IntResult, DestType))
+      return false;
+
+    return Success(IntResult, E);
+  }
   case CK_NoOp:
   case CK_LValueToRValue:
     return ExprEvaluatorBaseTy::VisitCastExpr(E);
@@ -10371,6 +10399,8 @@ bool ComplexExprEvaluator::VisitCastExpr(const CastExpr *E) {
   case CK_IntToOCLSampler:
   case CK_FixedPointCast:
   case CK_FixedPointToBoolean:
+  case CK_FixedPointToIntegral:
+  case CK_IntegralToFixedPoint:
     llvm_unreachable("invalid cast kind for complex value");
 
   case CK_LValueToRValue:

clang/lib/Basic/FixedPoint.cpp

@@ -218,4 +218,41 @@ APFixedPoint APFixedPoint::negate(bool *Overflow) const {
     return APFixedPoint(Sema);
 }
 
+llvm::APSInt APFixedPoint::convertToInt(unsigned DstWidth, bool DstSign,
+                                        bool *Overflow) const {
+  llvm::APSInt Result = getIntPart();
+  unsigned SrcWidth = getWidth();
+
+  llvm::APSInt DstMin = llvm::APSInt::getMinValue(DstWidth, !DstSign);
+  llvm::APSInt DstMax = llvm::APSInt::getMaxValue(DstWidth, !DstSign);
+
+  if (SrcWidth < DstWidth) {
+    Result = Result.extend(DstWidth);
+  } else if (SrcWidth > DstWidth) {
+    DstMin = DstMin.extend(SrcWidth);
+    DstMax = DstMax.extend(SrcWidth);
+  }
+
+  if (Overflow) {
+    if (Result.isSigned() && !DstSign) {
+      *Overflow = Result.isNegative() || Result.ugt(DstMax);
+    } else if (Result.isUnsigned() && DstSign) {
+      *Overflow = Result.ugt(DstMax);
+    } else {
+      *Overflow = Result < DstMin || Result > DstMax;
+    }
+  }
+
+  Result.setIsSigned(DstSign);
+  return Result.extOrTrunc(DstWidth);
+}
+
+APFixedPoint APFixedPoint::getFromIntValue(const llvm::APSInt &Value,
+                                           const FixedPointSemantics &DstFXSema,
+                                           bool *Overflow) {
+  FixedPointSemantics IntFXSema = FixedPointSemantics::GetIntegerSemantics(
+      Value.getBitWidth(), Value.isSigned());
+  return APFixedPoint(Value, IntFXSema).convert(DstFXSema, Overflow);
+}
+
 }  // namespace clang

clang/lib/CodeGen/CGExpr.cpp

@@ -4162,6 +4162,8 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) {
   case CK_IntToOCLSampler:
   case CK_FixedPointCast:
   case CK_FixedPointToBoolean:
+  case CK_FixedPointToIntegral:
+  case CK_IntegralToFixedPoint:
     return EmitUnsupportedLValue(E, "unexpected cast lvalue");
 
   case CK_Dependent:

clang/lib/CodeGen/CGExprAgg.cpp

@@ -853,6 +853,8 @@ void AggExprEmitter::VisitCastExpr(CastExpr *E) {
   case CK_IntToOCLSampler:
   case CK_FixedPointCast:
   case CK_FixedPointToBoolean:
+  case CK_FixedPointToIntegral:
+  case CK_IntegralToFixedPoint:
     llvm_unreachable("cast kind invalid for aggregate types");
   }
 }

clang/lib/CodeGen/CGExprComplex.cpp

@@ -509,6 +509,8 @@ ComplexPairTy ComplexExprEmitter::EmitCast(CastKind CK, Expr *Op,
   case CK_IntToOCLSampler:
   case CK_FixedPointCast:
   case CK_FixedPointToBoolean:
+  case CK_FixedPointToIntegral:
+  case CK_IntegralToFixedPoint:
     llvm_unreachable("invalid cast kind for complex value");
 
   case CK_FloatingRealToComplex:

clang/lib/CodeGen/CGExprConstant.cpp

@@ -876,6 +876,8 @@ class ConstExprEmitter :
     case CK_FloatingCast:
     case CK_FixedPointCast:
     case CK_FixedPointToBoolean:
+    case CK_FixedPointToIntegral:
+    case CK_IntegralToFixedPoint:
     case CK_ZeroToOCLOpaqueType:
       return nullptr;
     }

clang/lib/CodeGen/CGExprScalar.cpp

@@ -363,11 +363,14 @@ class ScalarExprEmitter
                        SourceLocation Loc,
                        ScalarConversionOpts Opts = ScalarConversionOpts());
 
+  /// Convert between either a fixed point and other fixed point or fixed point
+  /// and an integer.
   Value *EmitFixedPointConversion(Value *Src, QualType SrcTy, QualType DstTy,
                                   SourceLocation Loc);
   Value *EmitFixedPointConversion(Value *Src, FixedPointSemantics &SrcFixedSema,
                                   FixedPointSemantics &DstFixedSema,
-                                  SourceLocation Loc);
+                                  SourceLocation Loc,
+                                  bool DstIsInteger = false);
 
   /// Emit a conversion from the specified complex type to the specified
   /// destination type, where the destination type is an LLVM scalar type.
@@ -1225,17 +1228,25 @@ Value *ScalarExprEmitter::EmitScalarConversion(Value *Src, QualType SrcType,
   // TODO(leonardchan): When necessary, add another if statement checking for
   // conversions to fixed point types from other types.
   if (SrcType->isFixedPointType()) {
-    if (DstType->isFixedPointType()) {
-      return EmitFixedPointConversion(Src, SrcType, DstType, Loc);
-    } else if (DstType->isBooleanType()) {
+    if (DstType->isBooleanType())
+      // It is important that we check this before checking if the dest type is
+      // an integer because booleans are technically integer types.
       // We do not need to check the padding bit on unsigned types if unsigned
       // padding is enabled because overflow into this bit is undefined
       // behavior.
       return Builder.CreateIsNotNull(Src, "tobool");
-    }
+    if (DstType->isFixedPointType() || DstType->isIntegerType())
+      return EmitFixedPointConversion(Src, SrcType, DstType, Loc);
 
     llvm_unreachable(
-        "Unhandled scalar conversion involving a fixed point type.");
+        "Unhandled scalar conversion from a fixed point type to another type.");
+  } else if (DstType->isFixedPointType()) {
+    if (SrcType->isIntegerType())
+      // This also includes converting booleans and enums to fixed point types.
+      return EmitFixedPointConversion(Src, SrcType, DstType, Loc);
+
+    llvm_unreachable(
+        "Unhandled scalar conversion to a fixed point type from another type.");
   }
 
   QualType NoncanonicalSrcType = SrcType;
@@ -1443,19 +1454,17 @@ Value *ScalarExprEmitter::EmitScalarConversion(Value *Src, QualType SrcType,
 Value *ScalarExprEmitter::EmitFixedPointConversion(Value *Src, QualType SrcTy,
                                                    QualType DstTy,
                                                    SourceLocation Loc) {
-  assert(SrcTy->isFixedPointType());
-  assert(DstTy->isFixedPointType());
-
   FixedPointSemantics SrcFPSema =
       CGF.getContext().getFixedPointSemantics(SrcTy);
   FixedPointSemantics DstFPSema =
       CGF.getContext().getFixedPointSemantics(DstTy);
-  return EmitFixedPointConversion(Src, SrcFPSema, DstFPSema, Loc);
+  return EmitFixedPointConversion(Src, SrcFPSema, DstFPSema, Loc,
+                                  DstTy->isIntegerType());
 }
 
 Value *ScalarExprEmitter::EmitFixedPointConversion(
     Value *Src, FixedPointSemantics &SrcFPSema, FixedPointSemantics &DstFPSema,
-    SourceLocation Loc) {
+    SourceLocation Loc, bool DstIsInteger) {
   using llvm::APInt;
   using llvm::ConstantInt;
   using llvm::Value;
@@ -1472,13 +1481,26 @@ Value *ScalarExprEmitter::EmitFixedPointConversion(
   Value *Result = Src;
   unsigned ResultWidth = SrcWidth;
 
-  if (!DstFPSema.isSaturated()) {
-    // Downscale.
-    if (DstScale < SrcScale)
-      Result = SrcIsSigned ?
-          Builder.CreateAShr(Result, SrcScale - DstScale, "downscale") :
-          Builder.CreateLShr(Result, SrcScale - DstScale, "downscale");
+  // Downscale.
+  if (DstScale < SrcScale) {
+    // When converting to integers, we round towards zero. For negative numbers,
+    // right shifting rounds towards negative infinity. In this case, we can
+    // just round up before shifting.
+    if (DstIsInteger && SrcIsSigned) {
+      Value *Zero = llvm::Constant::getNullValue(Result->getType());
+      Value *IsNegative = Builder.CreateICmpSLT(Result, Zero);
+      Value *LowBits = ConstantInt::get(
+          CGF.getLLVMContext(), APInt::getLowBitsSet(ResultWidth, SrcScale));
+      Value *Rounded = Builder.CreateAdd(Result, LowBits);
+      Result = Builder.CreateSelect(IsNegative, Rounded, Result);
+    }
 
+    Result = SrcIsSigned
+                 ? Builder.CreateAShr(Result, SrcScale - DstScale, "downscale")
+                 : Builder.CreateLShr(Result, SrcScale - DstScale, "downscale");
+  }
+
+  if (!DstFPSema.isSaturated()) {
     // Resize.
     Result = Builder.CreateIntCast(Result, DstIntTy, SrcIsSigned, "resize");
 
@@ -1493,10 +1515,6 @@ Value *ScalarExprEmitter::EmitFixedPointConversion(
       llvm::Type *UpscaledTy = Builder.getIntNTy(ResultWidth);
       Result = Builder.CreateIntCast(Result, UpscaledTy, SrcIsSigned, "resize");
       Result = Builder.CreateShl(Result, DstScale - SrcScale, "upscale");
-    } else if (DstScale < SrcScale) {
-      Result = SrcIsSigned ?
-          Builder.CreateAShr(Result, SrcScale - DstScale, "downscale") :
-          Builder.CreateLShr(Result, SrcScale - DstScale, "downscale");
     }
 
     // Handle saturation.
@@ -2228,6 +2246,21 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     return EmitScalarConversion(Visit(E), E->getType(), DestTy,
                                 CE->getExprLoc());
 
+  case CK_FixedPointToIntegral:
+    assert(E->getType()->isFixedPointType() &&
+           "Expected src type to be fixed point type");
+    assert(DestTy->isIntegerType() && "Expected dest type to be an integer");
+    return EmitScalarConversion(Visit(E), E->getType(), DestTy,
+                                CE->getExprLoc());
+
+  case CK_IntegralToFixedPoint:
+    assert(E->getType()->isIntegerType() &&
+           "Expected src type to be an integer");
+    assert(DestTy->isFixedPointType() &&
+           "Expected dest type to be fixed point type");
+    return EmitScalarConversion(Visit(E), E->getType(), DestTy,
+                                CE->getExprLoc());
+
   case CK_IntegralCast: {
     ScalarConversionOpts Opts;
     if (auto *ICE = dyn_cast<ImplicitCastExpr>(CE)) {

clang/lib/Edit/RewriteObjCFoundationAPI.cpp

@@ -1086,6 +1086,8 @@ static bool rewriteToNumericBoxedExpression(const ObjCMessageExpr *Msg,
 
     case CK_FixedPointCast:
     case CK_FixedPointToBoolean:
+    case CK_FixedPointToIntegral:
+    case CK_IntegralToFixedPoint:
       llvm_unreachable("Fixed point types are disabled for Objective-C");
     }
   }